“Eat your fruits and vegetables” is not only your mother’s advice for your nutritional health but also the core message of the Dietary Guidelines for Americans, the official recommendations by the United States government for how its citizens should eat to stay healthy and slim.

“Healthy diets rich in fruits and vegetables may reduce the risk of cancer and other chronic diseases,” say the Centers for Disease Control and Prevention (CDC). Those other chronic diseases plague two thirds of our population and, increasingly, the rest of the world. Weight problems, diabetes, heart disease and hypertension keep spreading like wildfire around the globe and are killing tens of millions of people every year, according to the World Health Organization (WHO). These are mostly diet and lifestyle related ills, and much of the havoc they wreak could be avoided by changing our eating habits to what they once were before fast food and TV dinners. At least, that’s the thought.

While everyone seems to agree that eating fruits and vegetables is good for you, there is precious little knowledge among the public of what exactly makes fresh produce so beneficial. So, here are a few basic facts.

Fruits and vegetables are good sources of carbohydrates, a main component for dietary balance and health. Carbohydrates deliver energy to many bodily functions, including the brain and the nervous system. There are two groups of carbohydrates: simple and complex. Simple carbohydrates are provided by many fruits and also refined sugar. The complex kind are the ones you should opt for. Those are found in whole grains, starchy vegetables and legumes.

Fruits and vegetables also contain many vitamins and minerals. There are two categories of vitamins: fat-soluble, which get stored in the fat tissue, and water-soluble, dischargeable in the urine. Both are essential for growth, development and body functions. Minerals are important for the health of organs, tissue, bones, muscles and cells.

Fruits and vegetables are high in fiber, a carbohydrate, which paradoxically cannot be digested but is nevertheless important for the digestive process. A fiber-rich diet is believed to prevent cardiovascular disease and diabetes as well as certain types of cancer (although the latter has been disputed).

Fruits and vegetables are the main source of carotenoids (as in carrots) in most people’s diet. Carotenoids are responsible for the bright colors staring at you in the produce department and are believed to be highly beneficial, especially for eyesight.

Part of the nutritional value that sets fruits and vegetables apart are phytochemicals and antioxidants. Phytochemicals are plant chemicals whose multiple advantages are still being discovered. Antioxidants are substances that are believed to protect the body from so-called “free radicals,” metabolic byproducts that can cause cell damage, possibly leading to certain forms of cancer.

Unfortunately, many of these enormously valuable characteristics of the fruits and vegetables we commonly consume today have been diminished or altogether lost over time due to modern breeding and farming methods. In a recent article published in the New York Times, Jo Robinson, an investigative journalist and author of “Eating on the Wild Side: The Missing Link to Optimum Health” (Little, Brown & Co, 2013), reported on the substantial nutritional losses in our produce over the past 50 to 100 years. Because we largely abandoned gathering wild plants in favor of growing them domestically, she says, many of the nutrients were bred out to increase flavor and yield.

“Unwittingly, we have been stripping phytonutrients from our diet since we stopped foraging for wild plants some 10,000 years ago and became farmers,” she writes.

“Throughout the ages, our farming ancestors have chosen the least bitter plants to grow in their gardens. It is now known that many of the most beneficial phytonutrients have a bitter, sour or astringent taste. […] The more palatable our fruits and vegetables became, however, the less advantageous they were for our health.”

As a case in point, Robinson points out that corn, the way we prefer it today, namely sweet and of light or almost no color, has only a small fraction of the nutrients its ancestors had to offer.

“After reducing the nutrients in the majority of the fruits and vegetables we eat today, how can we recoup the losses,” she asks. Thankfully, there are still a few species around that have survived more or less intact, among them arugula salad leaves, green onions and a variety of herbs, now mostly used to enhance taste but still adding nutritional value.

In the end, of course, we have to work with what is available to us today. Compared to our dismal choices that dominate the so-called “Western diet,” consisting mainly of animal products and highly processed food, filling our plates with fruits and vegetables as much as possible remains the next best thing we can do to keep us healthy and properly nourished.